In general, a car body panel, for example, a center floor panel can satisfy a NVH (Noise Vibration Harshness) performance which is an item characteristic of habitability and comfort of a car only when the car body panel has a structure which can secure a rigidity as well as properly interrupt a noise entering a room.
The center floor panel is installed on a bottom of a middle portion in the car body, and has a structure which increases panel rigidity as well as interrupts the noise entering the room by forming at a regular interval a rigidity increasing foaming on the center floor panel constructed in one piece, and by attaching a pad on the center floor panel or carrying out a rust preventing coating treatment.
FIG. 1 shows a conventional center floor panel such as a curved panel structure having double curvatures, an embo panel structure, and a general bead structure.
However, the conventional structure was an efficient structure in the low frequency area but had a disadvantage in the intermediate frequency area and the high frequency area.
This structure had to apply a vibration reduction material to improve the intermediate frequency performance and the high frequency performance, thereby having a disadvantage in view of weight and cost.
Therefore, there is a need for an optimized structure preferable in view of weight and cost by minimizing the amount of application of vibration reduction material while securing the NVH performance not only in the low frequency area but also in the intermediate frequency area and the high frequency area.
Technologies which are background of the present invention are disclosed in Japanese laid-open patent publication Hei 9-202269, US laid-open patent publication 2006-163914, Japanese laid-open patent publication 2011-130174, and Japanese laid-open patent publication 2004-255983.
The above information disclosed in this Background section is only for enhancement of understanding of the background of the invention and therefore it may contain information that does not form the prior art that is already known in this country to a person of ordinary skill in the art.